The present invention relates to a document cover for protecting documents.
For custody/delivery of documents such as data, drawings, etc., the documents are sometimes covered with a document cover so as to be protected. Examples of a material for such a document cover include more or less thick woodfree paper, straw board, synthetic resin sheet material, composite paper, etc. In the case where the documents are covered with woodfree paper or straw board, the cover serving as a front cover can be folded easily by hand but it is difficult to form a straight fold line accurately. Accordingly, there has been provided a cover in which a guide depression line is formed in advance by means of pressure molding, or the like, in the portion where the fold line is to be formed.
However, such a paper cover per se is not suitable to carry because it has a disadvantage that it is susceptible to friction, low in durability and easy to get wet. When the document cover is formed of straw board, there is a disadvantage as follows. That is, the hold of the cover folded by hand cannot be released because the folded cover may be unfolded if the hold is released even in the case where a fold line is formed in advance in the cover so that the cover can be folded easily. On the other hand, a cover made of a synthetic resin sheet material or composite paper is suitable to carry not only because the synthetic resin sheet material or composite paper is incomparably higher both in abrasion resistance and in durability than paper but also because the synthetic resin sheet material or composite paper is water-resistant.
The synthetic resin sheet material is, however, greatly firm as compared with paper, so that the synthetic resin sheet material folded by hand may be unfolded soon even if the hold of the folded material is released. Therefore, fold lines are provided in a boundary portion between a front cover portion and a rear cover portion, and they are used to open the cover with documents fixed on the rear cover portion. Such a cover has no problem in binding thin documents but has a disadvantage that the front cover portion rises up when the documents are thick. This is because, in this case, a back portion having a width corresponding to the thickness of the documents is required to be provided in a boundary portion between the front and rear cover portions of the cover, but there is no fold line in a boundary portion between the front cover portion and the back portion.